The development of an optical transmission technology reveals a trend towards a higher rate on a single channel (e.g. a rate of 400 G/1 T on a single channel), a higher spectral efficiency and a high-order modulation format. Thus, the most clear and important development direction of the optical transmission technology still lies in increasing a transmission rate. High-speed transmission confronts a lot of limitations mainly in two aspects respectively described as follows. As regards the aspect 1, optical transmission technology is developing towards convergence transmission of high spectral efficiency and high-speed service interface transmission, if the spectral efficiency cannot be improved any longer, then the convergence of low speed services to a high-speed channel for transmission is not much meaningful. Nonetheless, there may be a high-speed Ethernet interface at a client side, the transmission problem of a high-speed interface still needs to be taken into consideration, thus, 400 G will be a critical point of the limit of spectral efficiency. As regards the aspect 2, as optical transmission technology is developing towards long-distance (long span and multi-span) transmission, the use of a low-loss fiber, a low-noise amplifier, reducing the cross section spacing and the application of other approaches, although capable of partly improving the Optical Signal-Noise Ratio (OSNR in short) of a system, cannot make a breakthrough, in addition, it is difficult to implement these approaches in engineering.
With the bandwidth of a bearer network required to be higher and higher, a beyond-100 G technology becomes a solution to the requirement for higher bandwidth. However, a Wavelength Division Multiplexing (WDM in short) of the conventional 50 GHz fixed grid cannot provide a sufficient spectrum width to realize a beyond-100 G technology, no matter a 400 G technology or a 1 T technology. In view of the defects in the fixed grid, a wider flexible grid is needed.
In related technologies, beyond-100 G multi-speed hybrid transmission and the flexibility of the modulation format for beyond-100 G transmission have different requirement on channel bandwidth, if a proper bandwidth is configured for each channel, then the bandwidth of a system can be fully used, thereby generating a flexible grid system. The requirement for an ultra high-speed WDM system brought by the demand for higher and higher bandwidth leads to a demand for a flexible grid technology, however, how to effectively plan and manage frequency spectrum and how to realize the compatibility of the introduced flexible grid technology to existing systems remain to be solved.
As to the problem on how to effectively plan and manage frequency spectrum after a flexible grid technology is introduced in related technologies, no effective solution has been proposed.